Vice-Admiral Shimizu, Mitsumi
The Sixth Fleet (Submarine) was commanded by Vice-Admiral Shimizu. On 29 July 1941 Admiral Isoroku Yamamoto (Yamamoto, Isoroku) ordered him to prepare to take part in the Hawaii Operation and to have his midget submarines ready for action. His command would operate independently of the First Air Fleet.
You can find out more about the Hawaii Operation in the following Osprey book: